It is the purpose of a telephone set to permit the transportation of speech over a distance by means of electric signals. At the transmitting end, the telephone set carries out a transformation of acoustic signals into electric signals. At the receiving end, the telephone set carries out the transformation of the electric signals into acoustic signals. The structure of a telephone set is well known. It comprises transducing elements for transforming the acoustic energy into electrical energy and vice versa, adapting elements for adapting to a transmission line and signaling and dialing elements. These elements are spread over a handset and a base station. Generally, the handset comprises the transducers, that is to say, a microphone and an earphone, and the base station comprises the other elements.
When two subscribers communicate with each other (referenced speaker and correspondent hereafter), there are a signaling phase and a conversation phase proper. During a conversation, the speaker may express himself in a sound environment which is more or less noisy. This noise is then transmitted to the correspondent by the telephone channel and will annoy the correspondent. Various techniques for eliminating the ambient noise of the signal to be transmitted have been described, for example, in the document entitled: "Frequency domain noise suppression approaches in mobile telephone systems", Jin Yang, IEEE International Conference on Acoustics, Speech and Signal Processing, Minneapolis, Apr. 27-30, 1993. But this does not resolve the problem of the speaker who is annoyed by the ambient noise around him. In effect, when the speaker receives the words sent by the correspondent, if the noise surrounding the speaker becomes heavy, the speaker can experience difficulties understanding the words of his correspondent.